The present invention is generally concerned with mobile radiocommunication systems.
The present invention is more particularly concerned with power control techniques used in such systems to improve performances (in terms of quality of service, of capacity, . . . etc.).
The present invention is in particular applicable to mobile radiocommunication systems of CDMA (xe2x80x9cCode Division Multiple Accessxe2x80x9d) type. In particular, the present invention is applicable to UMTS (xe2x80x9cUniversal Mobile Telecommunication Systemxe2x80x9d).
As is known, CDMA systems use two types of power control techniques, a so-called open-loop power control technique, and a so-called closed loop power control technique (also called hereinafter CLPC). These power control techniques may be recalled for example for the uplink transmission direction, i.e. from MS (xe2x80x9cMobile Stationxe2x80x9d) to BTS (xe2x80x9cBase Transceiver Stationxe2x80x9d). In the open-loop power control, a MS transmit power is controlled based on the power received by this MS from a BTS. In the CLPC, a MS transmit power is controlled based on the transmission quality of the link between this MS and a BTS, as estimated at this BTS.
The transmission quality of a link between a MS and a BTS depends on the ratio of the received signal power and the interference power, also called SIR (Signal-to-Interference Ratio). When the SIR of a MS is low, or equivalently when the powers of the other MSs are much higher than its power, its performances dramatically decrease. The CLPC algorithm enables to keep the SIR of each user as constant as possible.
The principle of the CLPC algorithm is that the BTS periodically estimates the SIR of the received signal from each MS, and compares this estimated SIR to a target SIR (SIRtarget). If the estimated SIR is lower than the target SIR, the BTS sends a power control command to the MS, for the MS to increase its transmit power. Otherwise, the BTS sends a power control command to the MS, for the MS to decrease its transmit power. The target SIR is chosen by the BTS as a function of the required quality of service.
To be efficient and track the variations of the SIR as closely as possible, in particular in fast changing environments, the CLPC needs to be rapid; as an example, in third generation systems like for example UMTS, power control commands are typically sent to a MS every slot in a frame (a slot being an elementary time unit in a packet data unit, or frame, transmitted in such a system, the frame duration being typically equal to 10 ms, and the slot duration to {fraction (1/16)} of the frame duration).
Now there are some situations in mobile radiocommunication systems, in which transmission of power control commands has to be momentarily interrupted. This will also hereinafter be referred to as transmission interruptions.
As an example, in CDMA systems, downlink transmission from a BTS to a MS may momentarily be interrupted to allow this MS to make measurements on frequencies other than the one used for this downlink transmission (in particular for handover preparation purposes, in particular inter-frequency handovers). Such a transmission mode including transmission interruptions is also referred to as xe2x80x9cslotted modexe2x80x9d or xe2x80x9ccompressed modexe2x80x9d in third generation systems like UMTS for example. A transmission interruption may last several slots. During these transmission interruptions, the CLPC is interrupted. Thus, the BTS does not send any more power control commands to the MS, and the uplink signals from this MS are no longer power controlled. Uplink transmission may simultaneously be interrupted, but in either case, as a result, the efficiency of the CLPC is significantly decreased, and the performances of the system may be seriously degraded.
In European patent application No. 99400894.4 filed on Apr. 12, 1999 (corresponding to U.S. application Ser. No. 09/302,985, filed Apr. 30, 1999) by Applicant, a solution has been proposed to avoid such degradations of performances, due to such transmission interruptions.
Essentially, according to this prior patent application, when transmission is resumed after a transmission interruption, said power control algorithm is implemented with at least one modified parameter, for a given duration, said at least one modified parameter and said given duration being determined so as to compensate for the effects of said transmission interruption on power control.
Said at least one modified parameter may in particular be an increased power control step size. In practice, to reduce the amount of signalling required to implement such a method, such an increased power control step size xcex42 may be fixedly set to a multiple (for example two times) of a power control step size xcex41 used otherwise.
Problems may arise, if the power control step size xcex41 is itself variable (for instance as a function of environment conditions or mobile speed for example). It may happen that the power control step size xcex41 currently in use when transmission is resumed is already large enough to achieve the result aimed at with such a method, and that an additional increase of the power control step size would on the contrary degrade the performances (for example, if xcex41 may take one of the two values 1 dB and 2 dB, and if xcex42=2. xcex41, xcex41=2 dB leads to xcex42=4 dB which may be too large).
The present invention enables to avoid such problems.
More generally, the present invention enables to better compensate for the effects of such transmission interruptions on power control, thereby improving performances.
Besides, the present invention enables such an improvement, while not increasing too much the amount of signalling required.
An object of the present invention is therefore a method for improving performances of a mobile radiocommunication system using a power control algorithm, wherein said system may be subject to transmission interruptions, said method comprising the steps of:
determining a preferred form in which said power control algorithm should better be implemented when transmission is resumed after a transmission interruption, to better compensate for the effects of said transmission interruption on power control,
implementing said power control algorithm in the thus determined form.
According to another object of the invention, said preferred form is determined as the preferred one among:
at least one modified form, wherein at least one parameter of said power control algorithm is modified, for a given duration, when transmission is resumed,
a non-modified form, wherein no parameter of said power control algorithm is modified when transmission is resumed.
According to another object of this invention, said modified and non-modified forms include different forms in which said algorithm may be implemented to adapt it to various conditions which may require such an adaptation.
According to another object of this invention, said conditions include environment conditions and/or mobile speed.
According to another object of this invention, said at least one parameter is the power control step size of said power control algorithm.
According to another object of this invention, said at least one modified parameter is an increased power control step size.
According to another object of the invention, said mobile radiocommunication system is of CDMA type.
According to another object of the invention, said power control is performed in the uplink transmission direction of said mobile radiocommunication system.
According to another object of the invention, said power control is performed in the downlink transmission direction of said mobile radiocommunication system.
According to another object of this invention, said power control algorithm involving a transmitting entity (mobile station or mobile radiocommunication network entity depending on whether said power control is performed in uplink or in downlink) and a receiving entity (mobile station or mobile radiocommunication network entity depending on whether said power control is performed in downlink or in uplink), said preferred form is determined in one of said entities, and sent, by means of signalling informations, to the other one of said entities, to be used by said other one of said entities.
According to another object of this invention, said signalling informations are transmitted together with transmission interruption commands.
According to another object of this invention, said signalling informations include a bit indicating which of a non-modified and a modified form is preferred.
According to another object of this invention, said signalling informations include additional bits indicating which of a plurality of modified forms is preferred.
According to another object of this invention, said preferred form is determined by one of said entities, and used locally by this entity, without any signalling to the other entity.
Another object of the present invention is a mobile radiocommunication network entity (such as in particular BTS) for performing such a method.
Another object of the present invention is a mobile station (MS) for performing such a method.
According to another object of the invention, a mobile radiocommunication network entity comprises, for performing said method in said uplink transmission direction:
means for determining a preferred form in which said power control algorithm should better be implemented when transmission is resumed after a transmission interruption, to better compensate for the effects of said transmission interruption on power control,
means for sending corresponding signalling informations to a mobile station.
According to another object of the invention, a mobile station comprises, for performing said method in said uplink transmission direction:
means for receiving such signalling informations from a mobile radiocommunication network entity.
According to another object of the invention, a mobile station comprises, for performing said method in said uplink transmission direction:
means for determining a preferred form in which said power control algorithm should better be implemented when transmission is resumed after a transmission interruption, to better compensate for the effects of said transmission interruption on power control.
According to another object of the invention, a mobile station comprises, for performing said method in said downlink transmission direction:
means for determining a preferred form in which said power control algorithm should better be implemented when transmission is resumed after a transmission interruption, to better compensate for the effects of said transmission interruption on power control,
means for sending corresponding signalling informations to a mobile radiocommunication network entity.
According to another object of the invention, a mobile radiocommunication network entity comprises, for performing said method in said downlink transmission direction:
means for receiving such signalling informations from a mobile station.
According to another object of the invention, a mobile radiocommunication network entity comprises, for performing said method in said downlink transmission direction:
means for determining a preferred form in which said power control algorithm should better be implemented when transmission is resumed after a transmission interruption, to better compensate for the effects of said transmission interruption on power control.